Interim Pension and Other Postretirement Benefit Plan Information (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
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| Pension Benefits | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | $ 2,580 | $ 2,837 | $ 5,160 | $ 5,674 |
| Interest cost | 6,925 | 6,663 | 13,850 | 13,326 |
| Expected return on assets | (7,949) | (7,655) | (15,898) | (15,309) |
| Amortization of prior service cost (credit) | 0 | 0 | 0 | 0 |
| Amortization of actuarial (gain) loss | (51) | 256 | (102) | 511 |
| Net periodic pension cost | 1,505 | 2,101 | 3,010 | 4,202 |
| Other Benefits | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | 2,017 | 2,033 | 4,034 | 4,066 |
| Interest cost | 3,635 | 3,365 | 7,270 | 6,731 |
| Expected return on assets | (4,070) | (3,831) | (8,140) | (7,663) |
| Amortization of prior service cost (credit) | (2,879) | (3,260) | (5,759) | (6,520) |
| Amortization of actuarial (gain) loss | (2,415) | (2,429) | (4,830) | (4,858) |
| Net periodic pension cost | $ (3,712) | $ (4,122) | $ (7,425) | $ (8,244) |
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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